1. Field of the Invention
The present invention relates to medical imaging system and method for generating medical images to be used for medical diagnoses, and specifically, relates to medical imaging system and method employing plural imaging apparatus such as a radiation mammography apparatus and an ultrasonic imaging apparatus.
2. Description of a Related Art
Recent years, breast cancer patients have been increasing not only in Europe and the United States but also in Japan. However, even when a breast has a cancer, early treatment can cure the breast cancer relatively easily without the need for breast amputation in many cases. Accordingly, apparatuses and systems for early detection of breast cancer are desired.
When a breast has a cancer, a tumor mass and calcification are produced in the breast. Therefore, finding the lesion parts as earlier in minimal size as possible leads to early detection of breast cancer. Currently, the mainstream technologies for the purpose are X-ray mammography examination and ultrasonic imaging examination. Here, X-ray mammography refers to a method of making medical diagnoses based on X-ray images obtained by using an X-ray imaging apparatus for breast (X-ray mammography apparatus). On the other hand, in ultrasonic imaging examination, ultrasonic images are generated based on reception data obtained by transmitting ultrasonic waves to an object to be inspected and receiving ultrasonic echoes reflected within the object, and the presence or absence of lesion is determined based on the ultrasonic images. The X-ray mammography and ultrasonic imaging have the following features, respectively.
X-ray mammography is suitable for exposing calcification as one of early symptoms of the cancer, and enables detection with high sensitivity and high resolving power. Further, in the case where mammary gland tissues have become atrophied and replaced with fat (so-called “fat breast”) as is the case of postmenopausal women, more information can be obtained by X-ray mammography. However, the X-ray imaging has a disadvantage that detection capability of specific natures of tissues (tissue properties) is low. Further, in an X-ray image, mammary glands are expressed in homogeneous soft tissue density, and thus, the detection of tumor mass is difficult in the case where mammary glands have developed (so-called, “dense breast”) as is the case of adolescent to premenopausal women. Furthermore, in X-ray mammography, only two-dimensional images in which the object as a solid is projected on a plane can be obtained. On this account, even when a tumor mass is found, it is difficult to take a sample for determination of benign or malignant lesion.
On the other hand, in ultrasonic imaging, specific natures of tissues (e.g., the difference between a cystic tumor and a solid matter) can be detected, and also a lobular cancer can be detected. Further, real time observation of images and three-dimensional image generation are possible. However, ultrasonic imaging examination often depends on the skill of an examiner (an operator such as a doctor) in accuracy and low in reproducibility. Further, it is difficult to observe minute calcification in an ultrasonic image.
As described above, X-ray mammography examination and ultrasonic imaging examination have both merits and demerits, and it is desirable that both examinations are performed for reliable detection of breast cancer.
As a related technology, U.S. Pat. No. 5,479,927 discloses a method and apparatus for generating ultrasonic images of the internal structure of breast tissue which images are in geometric registration with a mammogram by the combination of X-ray mammography and ultrasonic imaging. The apparatus includes a radiolucent (X-ray lucent) and sonolucent compression plate, and a gantry driven ultrasound transducer or a phased array ultrasonic transducer. Further, in the method, a mammogram and a plurality of corresponding ultrasound images are generated without moving the breast between the mammogram exposure and the ultrasound imaging.
However, in U.S. Pat. No. 5,479,927, by the combination of an X-ray mammography apparatus and an ultrasonic imaging apparatus, only two kinds of examination images correlated with respect to positions of the object or their synthesized images can be generated, but no effort is made to mutually utilize information obtained by the respective examination apparatuses.
Further, in either X-ray mammography or ultrasonic imaging, image statuses to be generated largely differ depending on imaging condition. However, appropriate imaging condition varies according to object statuses, and thus, it is often difficult to set appropriate imaging condition depending on skills of examiners.